Electrodeless vapor discharge lamp with auxiliary voltage triggering means



2 Shsets-$he9t l A GENTS W. A. MARRISON ELECTRODELESS VAPOR DISCHARGE LAMP WITH AUXILIARY VOLTAGE TRIGGERING MEANS July 20, 1965 Filed June 1, 1962 w mm w z T mm w mm j .1 M 66 5 .5 m M e B 2 w mw M Y/ i W w B //W% wafer, \QM 4 m 82 O 2 2 6 o E A 5 GM 6 2 my. WT W T WL Hm mm o g 9 4 K4 V///////////// L w w. 6 n 1 POWER SUPPLY SUPPLY VOLTAGE w. A. MARRISON 3 196 312 20, ELECTRODELESS VAPOR DISCHARGE LAMP WITH AUXILIARY VOLTAGE TRIGGERING MEANS 2 Sheets-Sheet 2 Filed June 1, 1962 HOOL HOb

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INVENTOR. BYW -M AGENT United States Patet O ELECTRQDELESS VAF'QR DISQHARGE LABW WHTH AUXILEARY VGLTAGE TREGGERlNG MEANS Warren A. Morrison, Palos Verdes Estates, Caiil'l, as-

signor, by mesne assignments, to Thompson Ramo ggoldridge Ind, (Zievelantl, @hio, a corporation of Filed liune 1, 1962, Ser. No. 199,384 6 Claims. (Cl. 315-171) This invention relates to light sources employing vapor discharge lamps, and more particularly to improved cans for triggering vapor discharge lamps of the kind that are devoid of internal electrodes and which receive energy of excitation from sources that are external of the lamp.

Electrodeless vapor discharge lamps are known in which light emission is produced through the ionizing action of electromagnetic fields on a vaporizable light radiating substance, such as a vapor confined in an envelope, the ionizing action being effected without the aid of electrodes in the envelope. Such a lamp is comparatively simple in structure, is inexpensive to build and operate, and generally has a relatively long life because of the absence of electrodes. One application of a vapor discharge lamp using an alkali metal vapor is in frequency standard work utilizing atomic resonance phenomena. The lamp may be used to provide optical pumping for a gas cell of the same alkali metal vapor as contained in the lamp to achieve highly accurate frequency control of a radiofreguency signal. The control is attained by detecting an error signal due to variation in signal frequency, and utilizing the error signal to correct the frequency of the radio-frequency signal.

The starting of such lamps has posed several problems. One reason for this is that the power that is required to start the lamp is too great for continuous operation. The power required to cause the initial ionization of gases within the lamp is enough to produce much too intense illumination in continuous operation, with resulting rapid deterioration of the lamp. it also produces a range of unwanted atomic transistions resulting in inefficient use of the input power.

Another reason is that it has been found expedient to use a low power transistor exciter oscillator circuit for the continuous operation, the oscillator circuit having insufficient power, when operated from its normal power supply, to produce the initial ionization.

Prior attempts to provide a satisfactory means for starting these lamps have resulted in some instances in the use of bulky and expensive equipment. In instances where the startin equipment has been simplified, the repeated use of such equipment has caused the lamps to deteriorate so that they become progressively more diflicult to start.

Accordingly, an object of this invention is to provide improved means for triggering electrodeless vapor dis charge lamps of the kind referred to without causing deterioration of the lamps.

A further object is to provide a simple, economical,

low power auxiliary means which can be used in conjunction with a low power, continuous energy source to trigger a vapor dischar e lamp, the auxiliary power means being thereafter de-energizable without affecting the continuous operation of the lamp.

The foregoing and other objects are realized according to the invention through the provision of an oscillator circuit which continuously generates and applies to the vapor discharge lamp an electromagnetic field whose magnitude is sufficient to sustain but insurficient to initiate ionization of the lamp vapors and light emission 'ice therefrom. Incorporated in the oscillator circuit is an auxiliary means for momentarily raising the voltage of the oscillator power supply so that the resulting increased field generated and applied to the lamp vapors is suflicient to initiate ionization and light emission therefrom. After the supply voltage is reduced to its normal value, the reduced electromagnetic field continuously applied to the lamp vapors is suflicient to sustain ionization and light emission.

In the drawings:

FIG. 1 is a view partly in section, partly schematic, showing a vapor discharge lamp in which the invention finds use;

FIG. 2 is a schematic of an oscillator circuit incorporating means for energizing a vapor discharge lamp according to the invention;

FIG. 3 is a graph illustrating operating voltages for the lamp;

FIG. 4 is a schematic circuit showing an alternative means for energizing the lamp;

FIG. 5 is a schematic circuit showing a further alternative means for energizing the lamp;

FIG. 6 is a schematic circuit showing yet another alternative means for energizing the lamp and employing a voltage doubler circuit; and

FIG. 7 is a schematic circuit similar to FIG. 6, but employing a transistorized switch.

FIGS. 1 and 2 illustrate one form of the invention as embodied in a light source intended for use with frequency control apparatus utilizing atomic resonance phenomena. However, it will become apparent that the principles of the invention are applicable to light sources useful in other environments, such as, for example, in the illumination of airport runways. The light source may be one of the kind disclosed in US. Patent No. 2,974,243. Referring to FIG. 1, the light source 1% includes a vapor discharge lamp 12. and a reflector 14 mounted within a housing 16. The interior of the housing 16 is provided with an annular shoulder 18 approximately at a central portion thereof for supporting a ring-like mounting bracket 2%. The bracket 26 has a lar e central opening 22, in which the reflector 14 is mounted, and several smaller openings 24 to reduce the cross section of the bracket 20 and thus to thermally insulate the reflector 14 from the housing 16.

The reflector 14-, which is made of an electrically conductive material, is generally funnel shaped, there being a neck portion 26 within which the lamp 12 is supported, and a flared portion 28 wedged within the central opening 2?. of the bracket 20. The flared portion 23 of the reflector 14 has an inner surface 29 formed with the appropriate curvature and a sufliciently bright surface texture to provide a desired reflection characteristic to the reflector 14. The inner surface 29 is given a parabolic curvature, for example, so that the light emitted by the lamp 12 from regions near the focal point P of the redoctor 14 will emanate from the reflector 14 as parallel rays.

The forward or flared end of the reflector 14 is formed with an annular shoulder 30 for supportin" a quartz window 31 that is transparent to the light emitted by the lamp 12. The window 31 serves in part as a dust cover for preventing foreign particles from depositing on the interior surface 29 of the reflector 14. Also, since quartz is a good reflector of long wavelength radiation, the window 31 serves to maintain a uniform temperature within the housing 16 by preventing the transmission of heat through the window 31. Both surfaces of the window 31 are preferably provided with anti-reflection coatings 32 and 34, for example of magnesium fluoride, so as to insure maximum transmission of the desired wavelength of light emitted from the lamp 12. The

window 31 and reflector 14 are fixed in position by means of an annular washer 36 of heat insulating material and a retaining ring 33 which is screwed into the forward end of the housing 16.

The discharge lamp 12 has an elongated cylindrical transparent envelope 40 made of glass, for example, one end portion of which is rigidly attached to the neck portion 26 of the reflector 14 by means of an intermediate cement layer 42, such as an epoxy resin, for example. The envelope 40 protrudes from the neck portion 26 into the cavity formed by the flared portion 28 of the reflector 14.

The lamp 12 contains a quantity of ionizable gas, which may be one of the noble gases such as argon, neon, helium, or krypton. In addition, the lamp contains a quantity of a vaporizable substance 44, preferably one of the alkali metals, such as rubidium, caesium, potassium, sodium, or lithium, which is stored on a metallic condensing member 46.

The condensing member 46, which may comprise a thin rod of substantially smaller diameter than that of the cylindrical envelope 40, is sealed through one end of the envelope 40 in axial alignment with the envelope 40. When made in rod form, the condensing member 46 may have a diameter that is to the size of the outside diameter of the envelope 40. The condensing member 46 is formed of a material that is easily wettable by the vaporizable substance 44. In addition, the condensing member material should be an electrical conductor. When a vaporizable substance 44 such as rubidium is used, the condensing member 46 may be of tungsten, for example.

The purpose of the condensing member is more fully described in the aforementioned US. Patent No. 2,974,- 243. It will suflice to say that the condensing member 46 functions to reduce noise in the lamp 12 by serving as a preferential collector of excess alkali metal vapor droplets which would normally condense on the envelope 40 wall surfaces. A heat sink 66 attached to the condensing member 46 maintains the temperature of the condensing member 46 slightly cooler than the envelope 40 walls so that the vapor droplets condense on the member 46 rather than the envelope 40 walls. 7

The condensing member 46 is surrounded by a heater 48 which is mounted on the neck portion 26 of the reflector 14. The heater 48 serves to maintain the vapor pressure of the alkali metal vapor'at the desired level at which light emission can occur when an energizing field is applied to the gas and vapor. The heater 48 may comprise a helical coil of insulation coated high resistance wire wound around the neck portion 26. A layer 50 of heat insulation material covers the heater coil 48. The heater 48 may be connected to a source of direct current voltage, not shown, to receive its heating current.

For supplying energizing electric fields to the lamp 12 an electromagnetic field producing element in the form of magnetic induction coil 56 is wound preferably around the end of the envelope 4t) opposite the end through which the condensing element 46 is sealed. One end of the coil 56 is spaced from the end of the condensing member 46 along the length of the envelope 40 so as to leave an intermediate envelope portion 58 that is free of both internal lamp structure as weil as external lamp structure. Furthermore, the lamp envelope 4%) is positioned axially within the reflector 14 so that a substantial part of the intermediate unobstructed envelope portion 58 will be centered at the focal point P of the reflector 14. Thus, during operation of the lamp 12, a substantial portion of high intensity light emission will issue from the lamp 12 at the focal point P of the reflector 14 and emanate from the reflector 14 as parallel light rays.

One connection to the induction coil 56 is made through a terminal 69 fastened and conductively connected to the flared portion 28 of the reflector 14. The

other connection to the coil 56 is made through apertures 4 62 and 64 in the reflector i4 and housing 116, respectively.

The energizing electric field for the continuous operation of the lamp 12 may be provided by connecting the induction coil 56 in a modified Colpitts oscillator circuit 67, as shown in FIG. 2. The induction coil 56, comprising several turns of wire wound around the end of the envelope 49, is connected in parallel with two series connected capacitors 68 and 7%, the latter capacitor 78 being connected to a common ground. The coil 56 and capacitors 68 and 79 form a tuned circuit. The junction of the capacitors 68 and 7t? is connected to the emitter 72 of a transistor 74. The collector 76 of the transistor is grounded. The high voltage end of the capacitor 68 is coupled through a capacitor 78 to the base 86 of the transistor 74. 7

Normal operating potentials are derived from a power supply 81 and voltage divider network comprising two resistors 82 and 84 connected across the terminals 85a and 85b. The base 8% of the transistor '74 is maintained at a positive potential relative to the collector by connection through an inductor 86 to the junction of the resistors 82 and 84. The emitter 72 is maintained at a slightly positive potential relative to the base 80 by connection through an inductor 88 and resistor 96 to the high voltage end of the resistor 84.

The normal power supply 81 for the oscillator circuit 67 is designed to deliver a voltage, for example 22 volts, which will produce an electromagnetic field in the coil 56 that is insuflicient by itself to initiate ionization of the vapor within the lamp 12. However, once the vapor is ionized to the point where substantial light emission is produced, by means which will now be described, the electromagnetic field generated in the coil 56 is of sufficient strength to sustain the ionization and light emission.

In accordance with the invention, an auxiliary voltage generating means is connected across the voltage divider resistors 82 and 84 to momentarily raise the power supply voltage thereacross and thereby produce an increased field in the coil 56. The increased field which appears momentarily in the coil 56 is suflicient to ionize the lamp 12 vapors to the extent of causing light emission therefrom. The auxiliary voltage generating means includes a direct current voltage source 92, having its negative terminal grounded, and connected in series with a switch 94 and a parallel connected capacitor 96 and resistor 98. A diode 100 connected between the positive terminal of the power supply 81 and the voltage divider resistor 84- isolates the power supply 81 from the auxiliary circuit. The size of the voltage source 92 is nominally about twice the voltage value of the power supply 81.

With the switch 94 open, the auxiliary circuit is disconnected from the oscillator circuit. The voltage appearing across the voltage divider resistors 82 and 84 is that furnished by the power supply 81, and is insufficient to initiate ionization of the lamp 12 vapors. In the graph of FIG. 3, the voltage level 102 corresponds to the magnitude of the supply voltage during an interval prior to the closing of the switch 94.

When the switch 94 is closed, the entire voltage of the source 22 momentarily appears across the voltage divider resistors 82 and 84. Since the voltage of the source 92 is approximately twice that of the power supply 81, the supply voltage appearing across the resistors 82 and 84 rises abruptly to a value that is twice the original voltage level 102. The increase in supply voltage is indicated by a sharply rising voltage pulse 164 in FIG. 2. As the capacitor 96 charges up to a value equal to the difference between the voltages of the source 92 and power supply 81, the supply voltage appearing across the resistors 82 and 84 drops by an equal amount. When the capacitor 96 is fully charged to the voltage difierence between the source '92 and the power supply 81, the voltage across the resistors 82 and 84 will have fallen to its original value, or voltage level 192.

, The voltage pulse 164 is of suflicient amplitude and duration to cause the vapors in the lamp 12 to achieve a fully ionized state and thereby emit light. The duration of the pulse 164 depends upon the capacitance value of the capacitor 96, the larger the capacitance the longer the pulse duration. At the termination of the pulse 1M, the reduced supply voltage at the lower level 1&2 will sustain ionization and light emission.

The mechanism by which the lamp 12 is ionized to produce light emission is as follows. When the oscillator circuit receives the voltage pulse Add, the alternating magnetic field produced axiall I of the induction coil 55 induces a circumferential electrical field at right angles to the magnetic field. The circumferential electric field is impressed upon the gas and vapor in the lamp 12. In addition to the circumferential electric field, there exists an alternating electric field between the high voltage end of the induction coil 56 (opposite the grounded end) and the reflector 14 (which is grounded). The reflector 14 thus constitutes a second electromagnetic field producing element, the first element being constituted by the induction coil 56. Since the composite of the two electric fields is concentrated in the central region 58 of the lamp 12 between the condensing member 46 and the induction coil 55, there will be a concentration of ionization produced in this region. Accordingly, the lamp will be triggered into light emission, with light of relatively high intensity being emitted from the focal point regions of the reflector 14.

The success of this method of starting the lamp 12 depends upon the ability of the transistor 7 to withstand, and to function briefly with, the increased voltage. A type 2Nll31 transistor has been found to operate successfully in this connection. When operated at room temperature, this type of transistor does not saturate at the double voltage involved, the duration of the voltage pulse 364 is so short that heat dissipation problems are not encountered.

If the switch 94 is left closed after the lamp 12 is operating, there will be a small leakage of current from the auxiliary voltage source 92 through the resistor $3 which will then supply a small part of the operating current normally supplied by the power supply 81. If the resistance value of resistor $8 is sufficiently high, the eli ect on the operation of the transistor oscillator circuit 67 will be negligible. Gthei'wise there is no requirement as to when the switch )4 is opened. If the switch 9 is opened after the lamp starting operation, the capacitor as will discharge through the resistor 98 and be ready for the next lamp starting operation.

The circuit of the invention was operated successfully with the following circuit values:

Coil 56 consisted of 23 turns of No. 25 enameled copper wire, wound with an inside diameter of approximately '7 millimeters.

While the direct current voltage source )2 has been shown as a battery in FIG. 2, it may be convenient to use other types of direct current voltage sources, such as rectifiers. PEG. 4, for example, shows a simple rectifier that can be used in place of the battery in this embodiment an alternating current source 1 36 is shown connected to a transformer the output of which is corn nected to one pair of terminals of a rectifier comprising four diodes little, 11%, little, and lllld. To the other terminals of the rectifier is connected a filter capacitor 112 across which the output rectified voltage is developed. The remainder of the circuit is the same as that of FIG. 1.

The power rating of this rectifier may be very small. However, the filter capacitor 112 should be large in comparison with the capacitor 96 in order to deliver nearly full voltage. Of course the loss in voltage due to charge sharing may be compensated by the use of increased rectifier voltage.

Another rectifier arrangement for producing an increased voltage of short duration is shown in FIG. 5. To the output of the rectifier diodes lllla lltld are connected a resistor 114, the capacitor 96, and a resistor 113. The capacitor as is connected to the diode 1% in series with the switch dd. in this case the auxiliary source, comprising the alternating current source 1% and the rectifier diodes llfiizell tl, delivers a voltage approximately equal to that of the power supply 81.

When the switch $4 is open, the only supply voltage delivered to the oscilltaor circuit 67 is that of the power supply 81. The capacitor 96 is fully charged by the rectiher, but the open switch 94 prevents the voltage of the capacitor 96 from being applied to the oscillator circuit 67.

When the switch 94 is closed the voltage appearing across the capacitor as is impressed in series with the voltage of the power supply 81. The capacitor 96 voltage appears momentarily as a pulse across the terminals a and 35b of the oscillator 67, the voltage quickly discharging through the oscillator circuit. The voltage pulse supplied by the capacitor 96 serves to trigger the vapor discharge lamp 12 in the same manner as the pulse 104 in FIG. 3. The resistors 114 and 118 are very large in resistance compared to the resistance appearing across the terminals 85a and 85b of the oscillator circuit 67 to achieve a long time constant in the rectifier charging circuit. Consequently, it is assured that the capacitor 96 will be almost completely discharged at the termination of the voltage pulse.

In the embodiment shown in FIG. 6, the desired voltage pulse is produced through a voltage doubler circuit connected between the power supply 81 and the oscillator circuit 67. In this circuit, a resistor 12% and capacitor 122 are connected in series across the negative terminal of the power supply and the diode Kill), respectively. Another capacitor 124 and resistor 126 are connected in series across the same points. The switch 94 is connected between the junction 127 of the resistor and capacitor 122 and the junction 128 of capacitor 12 and resistor 126.

When the switch 9d is open, each of the capacitors 122 and 124 is charged to the voltage of the power supply 81, which is insufiicient to trigger the lamp 12. When the switch 24 is closed, the capacitors 122 and 124 are connected in series aiding, and momentarily a voltage equal to twice the voltage of the power supply 81 is connected to the oscillator circuit 67, thereby triggering the lamp 12.

As long as witch 94 remains closed, the two capacitors 122 and 124, assumed to be equal, are connected in series across the power supply 81 and each remains charged to half of the power supply voltage. The two resistors 12% and 126, also equal, are connected in series across the power supply and constitute a small shunt load on the power supply inasmuch as the resistance values should be high.

At the termination of the starting pulse, the voltage supplied to the oscillator '67 is that of the power supply, whether or not the switch g4 remains closed. It is necessary, of course, to open the switch at some time prior to obtaining a new starting pulse in order to allow the capacitors to recharge to the full power supply voltage.

In this condition there is no steady flow of current through resistors 120 and 126.

solid state device may be used as a switch, as shown in FIG. 7. This circuit is the identical to that of FIG. 6, except that a solid state switching device 129 is substituted for the switch 94. The solid state switching device 129 includes a transistor 130, such as type 2N525, the collector 132 of which is connected to the junction point 127, and the emitter 134 of which is connected to the junction point 128. Between the base 136 and the emitter 134 is connected the secondary winding of a pulse transformer 138.

When a control pulse is applied to the input winding of the pulse transformer 138, the voltage pulse appearing in the output winding and applied between the base 136 and emitter 134 causes the resistance between the collector 132 and emitter 134 to drop to a very low value. The capacitors are thereby effectively connected together at the junction points 127 and 128. Otherwise, the operation of the circuit is identical to that of FIG. 6.

It is now apparent that the auxiliary voltage pulse generating means of the invention provides a simplified and economical means for starting an electrodeless vapor discharge lamp, while permitting a reduction in the continuous power requirements of the lamp.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 7

1. A vapor discharge light source, comprising:

a vapor discharge lamp including an'envelope;

a vaporizable substance within said envelope, the vapors of which are adapted to emit light of a characteristic wavelength when subjected to an electromagnetic field; a

said vapor discharge lamp being associated with a first predetermined level of electromagnetic field for initiating ionization of and light emission from said vapors;

said vapor discharge lamp being associated with a second predetermined level of electromagnetic field, that is lower than said first predetermined level, for sustaining ionization of and light emission from said vapors; w

an oscillator circuit including an output means coupled to said vapor discharge lamp for producing electromagnetic energizing fields for said lamp; 7

a main power supply for supplying a continuous operating voltage to said oscillatorcircuit to generate an electromagnetic field of said second predetermined level; and

an auxiliary voltage means connected between said oscillator circuit and said main power supply for supplying said oscillator circuit with a voltage pulse of sufficient magnitude to momentarily generate an electromagnetic field of said first predetermined level to initiate ionization of and light emission from said vapors;

said second level of electromagnetic field produced by said continuous operating voltage serving to sustain I said lamp after termination of said voltage pulse.

2. A vapor discharge light source, comprising:

a vapor discharge lamp including an envelope; 7 V

a vaporizable substance within said envelope; the vapors of which areadapted to emit light of a characteristic wavelength when subjected to an electromagnetic field;

m oscillator circuit including an output coil coupled to said lamp for producing an electromagnetic field for energizing 'said lamp vapors;

8. said oscillator circuit including a main power supply for supplying continuous operating voltage to said oscillator circuit to produce in said output coil an initial electromagnetic field of a magnitude that is insufiicient of itself to initiate ionization of and light emission from said vapors; and auxiliary means connected to said main power supply forapplying a voltage pulse additively to said continuous operating voltage to momentarily increase the electromagnetic field in said output coil to a magnitude suflicient to cause ionization of and light emission from said vapors; said initial electromagnetic field being of suflicient magnitude to sustain ionization of and light emission from saidvapors upon inactivation of said auxiliary means. 3. The invention according to claim 2, wherein said auxiliary means includes a diode connected to pass current from the positive terminal of said main power supply to said oscillator circuit; and

a pulse generating circuit connected across the supply terminals of said oscillator circuit;

said pulse generating circuit including, in series, a direct current voltage source, a switch, and a parallel connected capacitor and resistor combination,

said direct current voltage source being capable of delivering a voltage approximately equal to twice that of said main power supply.

4. The invention according to claim 2, wherein said auxiliary means includes a diode connected to pass current from the positive terminal of said main power supply to said oscillator circuit; and

a pulse generating circuit connected across said diode; said pulse generating circuit including a switch and a capacitor connected in series across said diode, and a source of rectified voltage connected in series with resistive means across said capacitor; said source of rectified voltage being capable of delivering a voltage approximately equal to that of said main power supply. 5. The invention according to claim 2, wherein said auxiliary means includes a diode connected to pass current from the positive terminal of said main power supply to said oscillator circuit;

a first capacitor and a first resistor connected in series between the negative and positive supply terminals, respectively, of said oscillator circuit;

a second resistor and a second capacitor connected in series between the negative and positive supply terminals, respectively, of said oscillator circuit; and

a switch connected between the junction of said first resistor and said first capacitor and the junction of said second resistor and said second capacitor.

6. The invention according to claim 5, wherein said switch includes a transistor having its collector connected to the junction between said second resistor and said second capacitor and its emitter connected to the junction between said first resistor and said first capacitor; and

means for applying an electrical switching signal between the base and the emitter of said transistor.

References Cited by the Examiner UNITED STATES PATENTS 2,118,452 5/38 Le Bel V 315248 2,149,414 3/ 39 Bethenod 315-248 2,549,828 3/51 Leppert 332-62 X 2,597,013 5/52 Marchetti 332-9 X 2,974,243 3/61 Marrison 315248 X FOREIGN PATENTS 24,610 9/ 35 Australia.

GEORGE N. W'ESTBY, Primary Examiner. 

1. A VAPOR DISCHARGE LIGHT SOURCE, COMPRISING: A VAPOR DISCHARGE LAMP INCLUDING AN ENVELOPE; A VAPORIZABLE SUBSTANCE WITHIN SAID ENVELOPE, THE VAPORS OF WHICH ARE ADAPTED TO EMIT LIGHT OF A CHARACTERISTIC WAVELENGTH WHEN SUBJECTED TO AN ELECTROMAGNETIC FIELD; SAID VAPOR DISCHARGE LAMP BEING ASSOCAITED WITH A FIRST PREDETERMINED LEVEL OF ELECTROMAGNETIC FIELD FOR INITIATING IONIZATION OF AND LIGHT EMISSION FROM SAID VAPORS; SAID VAPOR DISCHARGE LAMP BEING ASSOCIATED WITH A SECOND PREDETERMINED LEVEL OF ELECTROMAGNETIC FIELD, THAT IS LOWER THAN SAID FIRST PREDETERMINED LEVEL, FOR SUSTAINING IONIZATION OF AND LIGHT EMISSION FROM SAID VAPORS; AN OSCILLATOR CIRCUIT INCLUDING AN OUTPUT MEANS COUPLED TO SAID VAPOR DISCHARGE LAMP FOR PRODUCING ELECTROMAGNETIC ENERGIZING FIELDS FOR SAID LAMP; A MAIN POWER SUPPLY FOR SUPPLYING A CONTINUOUS OPERATING VOLTAGE TO SAID OSCILLATOR CIRCUIT TO GENERATE AN ELECTROMAGNETIC FIELD OF SAID SECOND PREDETERMINED LEVEL; AND AN AUXILIARY VOLTAGE MEANS CONNECTED BETWEEN SAID OSCILLATOR CIRCUIT AND SAID MAIN POWER SUPPLY FOR SUPPLYING SAID OSCILLATOR CIRCUIT WITH A VOLTAGE PULSE OF SUFFICIENT MAGNITUDE TO MOMENTARILY GENERATE AN ELECTROMAGNETIC FIELD OF SAID FIRST PREDETERMINED LEVEL TO INITIATE IONIZATION OF AND LIGHT EMISSION FROM SAID VAPORS; SAID SECOND LEVEL OF ELECTROMAGNETIC FIELD PRODUCED BY SAID CONTINUOUS OPERATING VOLTAGE SERVING TO SUSTAIN SAID LAMP AFTER TERMINATION OF SAID VOLTAGE PULSE. 